Biosynthesis of Nicotinamide Adenine Dinucleotide in Mitochondria

Abstract

Isolated rat liver mitochondria incorporate [14C]nicotinamide into NAD. Nicotinic acid and quinolinic acid are not utilized. The incorporation of nicotinamide into NAD is stimulated by ATP. After incubation of the mitochondria with [14C]nicotinamide, labeled NMN can be isolated. No labeling of nicotinate mononucleotide or nicotinate adenine dinucleotide could be observed. Azaserine has no effect on the incorporation of nicotinamide into NAD. Labeled NAD is also obtained after addition of [14C]ATP to the mitochondria. The incorporation of radioactivity from extramitochondrial [14C]ATP into NAD is inhibited by carboxyatractyloside. On the basis of these results, it is concluded that the mitochondria incorporate nicotinamide by an intramitochondrial biosynthetic pathway via NMN.